Panoramic refracting conical optic

ABSTRACT

An optical device having a semi-spherical or hemispherical field-of-view is provided. A conically-shaped piece of optical material has an annular surface satisfying Snell&#39;s Law for total internal reflection with respect to light passing through the piece and incident on the annular surface from within the piece.

This application is a division of application Ser. No. 09/616,624 filedon Jul. 28, 2000 now U.S. Pat. No. 6,424,470.

ORIGIN OF THE INVENTION

The invention was made by an employee of the United States Governmentand may be manufactured and used by or for the Government forgovernmental purposes without the payment of any royalties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to optical devices. More specifically, theinvention is an optical device capable of achieving a semi-spherical orhemispherical field-of-view.

2. Description of the Related Art

Imaging or illuminating cylindrical, semi-spherical or hemisphericalscenes is generally accomplished using a plurality of angularfield-of-view cameras/lenses positioned to characterize the necessaryfield-of-view. Typically, the angular field-of-view of each camera/lensis on the order of 120° or less. Thus, multiple cameras/lenses arerequired to simultaneously view or illuminate, for example, the trafficflow at an intersection, the entire area surrounding a vehicle orstructure, or the interior of a room or other structure.

A solution to this problem is a camera/lens having the ability to imageor illuminate annularly thereabout, i.e., over an entire 360°field-of-view. One such device is a panoramic annular lens (PAL)available commercially from Optechnology Incorporated, Gurley, Ala. ThePAL provides a cylindrical or flat annular image about an observationpoint. A two-dimensional diametrical view of the PAL is shown in FIG. 1and is referenced generally by 10. Accordingly, the three-dimensionalsolid structure of a PAL can be visualized by rotating PAL 10 about theZ-axis which passes through the central axis of PAL 10.

The two-dimensional representation of the flat annular image plane ofPAL 10 is represented by lines 12 and 14. That is, PAL 10 can be used toimage objects on either of lines 12 and 14. For example, the image pathfor an object on line 12 is indicated by path lines 16A-16D. Path 16Aindicates light traveling from line 12 (e.g., the surface of acylindrical object) to a convex surface 10A of PAL 10. Path 16Bindicates refracted light traveling from convex surface 10A through PAL10 to a convex surface 10B. Convex surface 10B is internally reflectiveso that path 16C indicates reflected light traveling from the reflectiveconvex surface 10B through PAL 10 to a reflective concave surface 10C.Path 16D indicates reflected light traveling from concave surface 10Cthrough PAL 10 to a flat clear surface 10D, at which point light exitsPAL 10. Note that a similar set of path lines could be drawn for anobject on line 14 with light entering PAL 10 at convex surface 10E andbeing reflected at convex surface 10F.

Unfortunately, the three-dimensional realization of a lens based on thetwo-dimensional diametrical geometry of PAL 10 is difficult to machinewith acceptable tolerances. Thus, the PAL based on the two-dimensionalgeometry described above is limited to use in expensive systems that cantolerate its high-cost of precision manufacturing. Further, the PAL'sforward-looking angular resolution along the Z-axis is limited due tothe presence of concave surface 10C.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anoptical device capable of being used to image or illuminate a 360°field-of-view.

Another object of the present invention is to provide an optical devicehaving a field-of-view that is semi-spherical or hemispherical.

Still another object of the present invention is to provide a 360°field-of-view optical device of simple construction.

Other objects and advantages of the present invention will become moreobvious hereinafter in the specification and drawings.

In accordance with the present invention, an optical device has at leasta semi-spherical field-of-view. The device comprises a conically-shapedpiece of optical material having an annular surface satisfying Snell'sLaw for total internal reflection with respect to light passing throughthe piece and incident on the annular surface from within the piece. Theannular surface is symmetric about the device's longitudinal axis withits exterior being concave.

BRIEF DESCRIPTION OF THE DRAWING(S)

Other objects, features and advantages of the present invention willbecome apparent upon reference to the following description of thepreferred embodiments and to the drawings, wherein correspondingreference characters indicate corresponding parts throughout the severalviews of the drawings and wherein:

FIG. 1 is a two-dimensional diametrical view of a prior art panoramicannular lens (PAL) illustrating the path of light movement therethrough;

FIG. 2 is a two-dimensional diametrical view of the panoramic refractingoptic according to the present invention illustrating the path of lightmovement therethrough;

FIG. 3 illustrates another embodiment of the present invention having aconcave end face;

FIG. 4 illustrates another embodiment of the present invention having aconvex end face;

FIG. 5 illustrates another embodiment of the present invention having acylindrical extension with a flat outboard end;

FIG. 6 illustrates another embodiment of the present invention having acylindrical extension with a concave outboard end;

FIG. 7 illustrates another embodiment of the present invention having acylindrical extension with a convex outboard end;

FIG. 8 illustrates another embodiment having of the present invention anaperture with a field-of-view along the optic's longitudinal axis; and

FIG. 9 illustrates still another embodiment of the present inventionhaving an aperture with a field-of-view along the optic's longitudinalaxis.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring again to the drawings, and more particularly to FIG. 2, atwo-dimensional diametrical view of an embodiment of a panoramicrefracting optic according to the present invention is shown andreferenced generally by numeral 100. That is, the three-dimensionalsolid structure of the optic is achieved by rotating the view in FIG. 2about the longitudinal axis 102 of optic 100. Accordingly, the presentinvention is a solid, conically-shaped, three-dimensional structure.Optic 100 is made from any optical material that permits the passage oflight therethrough. Suitable materials include, but are not limited to,quartz glass, plexiglass, flint glass, boron glass, diamond, or anyother optical material suitable for use in the manufacturing of lenses.

In the description to follow, optic 100 will be explained for its use inimaging objects lying in a semi-spherical or hemispherical scene aboutoptic 100. However, it is to be understood that optic 100 could also beused to illuminate objects in this same scene simply by supplying lightenergy in the reverse direction of the imaging light paths. Accordingly,optic 100 can be used by itself or in conjunction with a camera ordisplay device (not shown) for purpose of imaging, or could be used inconjunction with a light source (not shown) for purpose of illumination.

A conically-shaped annular portion of optic 100 is represented in FIG. 2by concave surfaces 104 and 106 which meet at a vertex 108 and terminateat a flat face 110 opposite vertex 108. While the shape of surfaces 104and 106 are identical, the particular geometry thereof can vary. Forexample, surfaces 104 and 106 could be defined by the arc of a circle, aparabola, an ellipse, etc., as long as the following criteria are met.The criteria will be explained by describing the movement of lightthrough optic 100.

An object 20 to be imaged lies on a semi-spherical region defined bydashed line 22. Light reflected by object 22 travels along path 24A in atransmission medium 101 (e.g., air, water, etc.) and is incident uponthe outer portion of surface 104. The light refracts slightly andtravels along path 24B through optic 100 and is incident on the innerportion of surface 106 at a point of incidence 27 of light. A surfacenormal 28 is defined. Surfaces 104 and 106 are shaped such that lightpassing through optic 100 and incident on surface 104 or 106 (i.e., theconically-shaped annular portion of optic 100) will be totallyinternally reflected. In the illustrated example, this means that lighttraveling along path 24B is totally internally reflected at point 27towards flat face 110 along path 24C. Note that light along path 24C isslightly refracted at as it exits flat face 110. However, the amount ofrefraction is small because the surface normal and light path are nearlyaligned. Therefore, the refraction at face 110 does not affect thefunction of optic 100.

To achieve total internal reflection at the inner portion of surfaces104 and 106, Snell's Law for total internal reflection must be satisfiedall along surfaces 104 and 106. That is, the angle θ between path 24B atpoint of incidence 27 and surface normal 28 must be greater than thecritical angle θ_(c) defined by Snell's Law which states

sin θ_(c)=(n ₁ /n ₂)  (1)

where n₁ is the index of refraction for transmission medium 101, and

n₂ is the index of refraction of the material used for optic 100.

Thus, for total internal reflection,

θ>θ_(c)   (2)

or

θ>sin⁻¹(n ₁ /n ₂)  (3)

The present invention is not limited to the specific constructiondescribed for optic 100. For example, the end face (i.e., face 110) neednot be flat, but could be a concave face 112 (FIG. 3) or a convex face114 (FIG. 4). Shaping of the end face can be used to tailor the exiting(or entering in the case of illumination) light path for a particularapplication. Still further, the conically-shaped annular portion of theoptic could have a cylindrically-shaped piece of optical materialoptically coupled thereto (i.e., integral therewith) as shown in FIGS.5, 6 and 7. In FIG. 5, a cylindrical portion 116 having an outboard endwith a flat face 116A extends from the conically-shaped annular portiondefined by surfaces 104 and 106. In FIG. 6, a cylindrical portion 118having an outboard end with a concave face 118A extends from theconically-shaped annular portion defined by surfaces 104 and 106. InFIG. 7, a cylindrical portion 120 having an outboard end with a convexface 120A extends from the conically-shaped annular portion defined bysurfaces 104 and 106. The inclusion of the cylindrical portion providesa means for holding the optic during the manufacturing and use thereof.

In each of the above-described embodiments, the optic's conically-shapedannular portion defined by surfaces 104 and 106 terminates in vertex108. However, in situations where a full hemispherical field-of-view isneeded, an optical aperture defining a field-of-view along the optic'slongitudinal axis can be incorporated into the optic of the presentinvention. For example, in FIG. 8, a clear aperture or lens 130 isincorporated into the tip of the conically-shaped annular portiondefined by surfaces 104 and 106. Aperture 130 could also be incorporatedon the end of a cylindrical extension 132 as shown in FIG. 9. Aperture130 has a field-of-view along longitudinal axis 102 so that ahemispherical region defined by dashed line 23 can be imaged orilluminated. More specifically, the field-of-view of theconically-shaped annular portion defined by surfaces 104 and 106 mightbe in the semi-spherical region 23B. Note that any embodiment includingaperture 130 can have a flat end face 110, a concave face 112 as in FIG.3, a convex face 114 as in FIG.4, a cylindrical portion 116 as in FIG.5, a cylindrical portion 118 as in FIG. 6, or a cylindrical portion 120as in FIG. 7.

The advantages of the present invention are numerous. The optic canimage or illuminate a semi-spherical or hemispherical region thereabout.The conically-shaped optical can be constructed easily as it is a simplegeometry to machine.

Although the invention has been described relative to a specificembodiment thereof, there are numerous variations and modifications thatwill be readily apparent to those skilled in the art in light of theabove teachings. It is therefore to be understood that, within the scopeof the appended claims, the invention may be practiced other than asspecifically described.

What is claimed as new and desired to be secured by letters patent ofthe united states is:

What is claimed is:
 1. An optical device comprising a conically-shapedpiece of optical material having an annular surface satisfying Snell'sLaw for total internal reflection with respect to light passing throughsaid conically-shaped piece to be incident on said annular surface,wherein said optical device has at least a semi-spherical field-of-view,wherein said conically-shaped piece terminates longitudinally at a firstend thereof in a vertex and in a second end opposite said first end; acylindrical piece of optical material optically coupled to said secondend, said cylindrical piece extending to an outboard end thereof anddefines a convex surface at said outboard end.
 2. An optical devicecomprising a conically-shaped piece of optical material having anannular surface satisfying Snell's Law for total internal reflectionwith respect to light passing through said conically-shaped piece to beincident on said annular surface, wherein said optical device has atleast a semi-spherical field-of-view, wherein said conically-shapedpiece terminates longitudinally at a first end thereof and in a secondend opposite said first end; an optical lens optically coupled to saidfirst end, said optical lens having a field-of-view that issubstantially forward of said first end; a cylindrical piece of opticalmaterial optically coupled to said second end of said conically-shapedpiece, said cylindrical piece extending to an outboard end thereof,wherein said cylindrical piece defines a convex surface at said outboardend.